Some processes are already known (cf. Swiss Patent Specifications Nos. 426,601 and 473,741 and International Patent Application No. PCT/CH79/00128) for manufacturing foamed granular glass from pulverized glass, with the addition of a blowing agent releasing gas at higher temperatures.
Thereby, for preparing foamed granular glass, it was necessary first to grind the raw material to a powder, to mix this powder with a blowing agent releasing gas in heat, and to form raw granules from the so obtained mixture. The raw granulated material so obtained was then, appropriately together with a parting agent, preheated and blown in a furnace or on a drying belt.
The foamed granulated glass manufactured in this manner had an inhomogeneous structure insofar as the size and the distribution of the cells were different in the surface area of each granule from those in its interior. This fact led to a decrease in compressive strength in the surface area of each granule, and thereby to a decrease in the total compressive strength.
Furthermore, some processes were also described (cf. Luxemburgian Patent Specification No. 79,661, German Published Patent Applications Nos. 2,206,448 and 2,224,009) for manufacturing blocks or plates of foamed glass which, if desired, could be broken down to a granulate. These publications, however, do not contain any indication with respect to the physical or mechanical properties of the granulated material. However, it is clear to the person skilled in the art that by the described processes only relatively coarsely porous products, having a low number of cells and an ununiform size of cells, a relatively high specific weight and a low compressive strength may be obtained.